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Full text of "Text Book Of Mechanical Engineering"

Core Boxes and Prints.

55

is carefully varnished so as to preserve it  from   moisture,   and
present a smoother surface to the mould.

Core Boxes.—The simplest kinds are such as are shewn at
Figs. 8, 10, and 14, where half the core lies in
each box. Pegs to unite them are formed by
knocking rough rods of wood through the steel
plates, Fig. 68, and then driving these into holes
in the core boxes (see a, Fig. 69). The pegs need
not have more than a quarter or five-sixteenths
of-an-inch projection, as, if they are longer, they
may stick. The exact correspondence of peg
and socket is found by pressing some little
object, such as a pinhead, between the boxes,
and using these marks as centres. Pegs are
also required to unite the halves of patterns. Wooden pegs
are now greatly superseded by brass dowels (Fig. 6&a).

The hollows of cylindrical core boxes are gauged by the use
of a property of the semi-circle—viz.,
that the angle contained by it is always a
right angle. So that the box may be
gouged out as in Fig. 69, and tried from
time to time with a set square.

More complicated core boxes have
been already drawn at Figs. 30, 31, 33,
and 41. The last one may be noticed as
a case of a box that must be loose on
every side in order to effett the safe
removal of the core.

Core Prints.—At this point we may
consider shortly the different kinds of core
prints.

Simple cylindrical core prints are shewn at Figs. 10, 15, 18,
37 : they require a slight taper in direction of withdrawal. Some-
times it is necessary for economy to core the bolt holes in the
flange of a steam pipe, especially if the holes are to be square
A little consideration here of direction of withdrawal will
show that, if we used prints, they would need to be of a very
special kind, so they are usually dispensed with altogether,

. 68 a^.